Báo cáo khoa học: Taxonomical impact of morphological variation in Quercus robur and Q petraea: a contribution to the hybrid controversy

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Báo cáo khoa học: " Taxonomical impact of morphological variation in Quercus robur and Q petraea: a contribution to the hybrid controversy" Original article Taxonomical impact of morphological variation in Quercus robur and Q petraea: a contribution to the hybrid controversy G Aas Chair of Forest Botany, 8050 University of Munich, Hohenbachernstr, 22, Freising 12, GermanySummary —Numeric - taxonomical analysis of the complex Quercus robur-Q petraea showed thatvariability within each of the 2 species is so wide that none of the features considered is suitable forclear distinction. By using multivariate statistical analysis, it was possible to differentiate 2 distinctgroups and thus to locate intermediate individuals. However, designating such morphologically inter-mediate individuals as hybrids remains questionable because it is not possible to find the exact limitsof each group. For practical reasons, such limits have often been defined more or less arbitrarilywithout taking into account the wide variability of the 2 species. This explains the widely acceptedview that they hybridize frequently, a view that cannot be supported by the findings of this project.Quercus robur / Quercus petraea /taxonomy / morphological variation/ hybridizationRésumé — Impact taxonomique de la variation morphologique chez Quercus robur et Q pe-traea : une contribution à la controverse sur les hybrides. L’analyse taxonomique numérique ducomplexe Quercus robur-Q petraea montre que la variabilité à l’intérieur de chacune des 2 espècesest si grande qu’aucune des caractéristiques considerées ne permet une claire démarcation. En utili-sant les statistiques multivariées, il a été possible de différencier 2 groupes distincts et ainsi de loca-liser les individus intermédiaires. Pourtant, désigner de tels individus morphologiquement intermédi-aires comme hybrides reste contestable, parce qu’il n’est pas possible de définir une limite exactepour chaque groupe. De telles limites ont souvent été définies, pour des raisons pratiques, demanière plus ou moins arbitraire. Elles ne tenaient pas compte de la grande variabilité des deuxespèces. Cela explique l’opinion répandue selon laquelle elles s’hybrident fréquemment, opinion quine peut être soutenue par les résultats de cette étude.Quercus robur/Quercus petraea / taxonomie / variation morphologique / hybridation* Present address: Chair of Forest ETH Zentrum, CH-8092 Zürich, Swit- Pathology and Dendrology,zerlandINTRODUCTION trees, ie, trees that at the time of sampling could not be assigned to the respective species. For this reason, some stands were examined specif-Pedunculate and sessile oak (Quercus ro- ically for such trees, and 33 of them (12%) werebur L, and Q petraea (Matt) Liebl) can hy- included in the total of 279 trees.bridize, a fact proved by numerous cross- For each tree the following 10 characteristicsing experiments (Dengler, 1941; Rushton, examined: 1) length of petiole (mm); 2) were length of lamina (mm); 3) width of lamina (mm);1977; Aas 1991).However, deductions on 4) shape of lamina (width at 0.25 length of lami-the frequency of hybridization under natu- na / width at 0.75 length); 5) depth of sinusesral conditions different matter. Inves- are a (index value); 6) leaf base (5 shape values rang-tigations on this subject revealed different ing from 0=extremely cordate to 4= tapering); 7)results (see review in: Gardiner, 1970; Ols- number of lobes; 8) sinus-veins (relative fre-son, 1975; Wigston, 1975; Rushton, 1978, quency of lateral veins running to sinuses in the middle portion of the leaf; values obtained1983; Dupouey, 1983: Kissling, 1983; ranged from 0 to 1.0 absent on all leaves, 1Grandjean and Sigaud, 1987). = = present on all leaves, 0.3 present on 3 out of ...